1. Field of the Invention
The present invention relates to a method and apparatus for reporting carrier status, and more particularly, to a method and apparatus for reporting carrier status in a user equipment of a wireless communication system, so as to reduce waste of radio resources and power consumption of the user equipment, and enhance the system performance.
2. Description of the Prior Art
Long Term Evolution wireless communication system (LTE system), an advanced high-speed wireless communication system established upon the 3G mobile telecommunication system, supports only packet-switched transmission, and tends to implement both Medium Access Control (MAC) layer and Radio Link Control (RLC) layer in one single communication site, such as in base stations (Node Bs) alone rather than in Node Bs and RNC (Radio Network Controller) respectively, so that the system structure becomes simple.
However, to meet future requirements of all kinds of communication services, the 3rd Generation Partnership Project (3GPP) has started to work out a next generation of the LTE system: the LTE Advanced (LTE-A) system. Carrier aggregation (CA), where two or more component carriers are aggregated, is introduced into the LTE-A system in order to support wider transmission bandwidths, e.g. up to 100 MHz and for spectrum aggregation. Using CA, the network of the LTE-A system provides multiple component carriers instead of a single component carrier for a UE, to establish multiple links for simultaneously receiving and transmitting on each component carrier.
At present, the characteristics of CA are quoted as below:
(1) Supporting CA for both contiguous and non-contiguous component carriers.
(2) It is possible to configure a UE to aggregate a different number of component carriers in the uplink (UL) and the downlink (DL), to obtain different bandwidths.
(3) From a UE perspective, there is one transport block and one hybrid-ARQ (HARQ) entity per scheduled component carrier.
In addition, to configure component carriers of the UE, the network outputs radio resource control (RRC) signaling to the UE, e.g. RRC Connection Setup message or RRC Connection Reconfiguration message.
After CA is configured, the UE has to monitor DL component carriers configured and activated by the upper layer, e.g. RRC, so as to obtain scheduling or control information, and perform transmission or reception accordingly. However, in some situations, transmission amounts may be suddenly increased or decreased, and thus, the network needs to activate or deactivate a part of component carriers of the UE. In general, the network uses a medium access control (MAC) control element (CE), to indicate the UE to activate or deactivate specified component carriers. Thus, the network can determine whether the MAC CE is successfully received by the UE according to feedback messages of HARQ. However, if a NACK (non-acknowledgement) to ACK (acknowledgement) error or DTX (discontinuous transmission) to ACK error occurs, the network erroneously determines that the UE has received the MAC CE. In such a situation, if the MAC CE that is not successfully received by the UE is to activate UL component carriers, the UE does not monitor the corresponding physical downlink control channel (PDCCH), and cannot receive transmission grant indicated by the network via PDCCH, causing waste of radio resources. If the MAC CE is to activate DL component carriers, the UE does not monitor the corresponding PDCCH, and cannot receive DL data, causing data lost. Oppositely, if the MAC CE is to deactivate UL or DL component carriers, the UE keeps monitoring PDCCH, causing unnecessary power consumption.
As can be seen, after CA is configured, if the signaling for activating or deactivating carries is not successfully received, waste of radio resources or unnecessary power consumption of the UE is occurred. Therefore, there is a need to enhance reliability of the signaling.